Mixture control apparatus



NCW 13, 1945- D. J. DESCHAMPS I MIXTURE co'NTRoL- APPARATUS 15 Sheets-Sheet 1 Filed March 13, 1943 y ATTORNEYS Nov. v13, 1945. D, J, DESCHAMPS 2,388,681

MIXTURE CONTROL APPARATUS Filed March 13, 1945 15 Sheets-sheet 2 NOV- 13 1 945- D. J. DESCHAMPS MIXTURE CONTROL APPARATUS Filed March 13, 1943 15 Sheets-Sheet 5 WIW 53M ATTORNEYS Nov. 13, 1945. p. J. DESCHAMPS .2,388,681

I' MIXTURE CONTROL APPARATUS Filed March 13, 1945 15 Sheets-Sheet 4 ATTORNEYS Nov. V113, 1945. D. J. DESCHAMPS 258mm MIXTURE CONTROL APPARATUS Filed March 13., 1945 V 15 Sheets-Sheet 5 l N l $5 Q A INVENTOR ATTORN EYS NOV. 13, 1945. D- 1 DESCHAMPS 2,388,68l Y MIXTURE CONTROL APPARATUS Y y y Filed March 13, 1943 15 Sheets-Sheet 6 ATTO R N EY5 Nov.18,1945. .M DESCHAMPS 2,388,681

MIXTURE CONTROL APPARATUS Filed March 13, 1943 l5 Sheets-Sheet '7 ATTORN EY5 NOV- 3, 1945- D. J. DESCHAMPS MIXTURE CONTROL APPARATUS Filed March 13, '1945 15 sheets-sheet 8 Mg M ATTORN EY NOV' 13 1945- D. J. DESCHAMPS MXTURE CONTROL APPARATUS Filed March 13, 1945 15 Sheets-ShamI 9 @n f ,SQ www wg SQ Q T L lNVENTOR Nov. L3, N45. p. .1 -DESCHAMPS MIXTURE CONTROL APPARATUS Filed March 13, 1943 15 Sheets-Shave?. l0

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Nov. 13, 1945. D. J. DESCHAMPS MIXTURE oNfrRoL APPARATUS Filed March 15, 1943 15 sheets-sheet 15 WM .f M

ATTORNEYS PaientedNov. 13, "1945 Desire J. Deschamps, Rutherford, J., assignerto Deschamps Fuel Injection Corporation, New York, N. Y a corporation of New York Application March 13, 1943, Serial N0. 'ii'lrhlidd 4': claims. (ci. 12s-iis) This invention relates to fuel` mixture control apparatus for internal combustion engines which operate on the Otto cycle, the object of the invention being to provide a generally improved mixture control mechanism for such engines.

The function of vmixturecontrol apparatus is to provide an automatic control of thesupply, 'or' feed, of the liquid fuelv in relation to the air ticular engine, or type of engine, `and these changes in pressure and speed may be shown on a graph or curve expressing precisely thepattern which the change in fuel-air ratio should follow charge to produce. a suitable ratio of fuel and air for the proper operation of the engine; The apparatus of the present invention is intended for use in connection with engines of the type i'n which the fuel mixture is formed in the air in,

take conduit of -the engine externally of the engine'cylinders, by the injection into such conduit of liquid fuel 'under appropriate pressure, and, also for use with engines of thetype in which the fuel is injected directly into the engine cylinders.

The invention relates more particularly tofuel mixture control apparatus in which the fuel is supplied by a variable capacity pump driven by the engine, the Aoutput of'which, at any given setting of its capacity control lever, therefore, increases or decreases substantially in proportion to increase'or decrease of the engine speed, and in which the pump capacity control lever is adjusted or controlled in response to the variatain operating conditions of the aircraft for the' tions in the uid pressure and temperature inv the intake conduit between the air throttle and the engine cylinders. Variations' in such fluid pressure occur as the engine is operated under varying conditions of speed and power, and such` temperature variations occur as the engine is operated under different conditions of atmospheric temperature.

It has heretofore been recognized' that the fuelair ratio at both-the lower4 and upper ends vof the speed and power `range of the engine should be higher than throughout the intermediate speed and power range. In fact such a fuel-air mixture characteristic is obtained, in a degree at least, even with certain types of suction carburetors."

However, the arrangements heretofore 4proposedin connection with fuel injection engines for providing automatic change of the fuel-air ratio with increase or decrease of engine speed Y the pilot to change the setting of the automatic and power (corresponding to different positions of the engine throttle and different manllfold pressures) have been inadequate,and the present invention aims, among other objectives, to overcome this deficiency. In every internal'combustion engine, or type of internal combustion engine, the pressure in the air inductionV pipe varies with change in speed and power in a manner or fashion which'is characteristic of that pai.'-

from the engine idling speed, through cruising speed and power and to maximum speed and power. The present invention aims to provide a mixture control apparatus which automatically will control the mixture to providethe correct fuel and air ratio throughout the ,entire speed and power range of the engine accordance with such characteristic 'pattern of lthe particular engine, or typeof engine, `so that at all speeds theengine will be suppliedwith fuel and air in correctl proportions merely by manipulation of the air throttle lever. This is of considerable importance to a combat aircraft pilot as it ellminates the necessity of his operating a second lever in order to obtain full power from the engine.

However, in the operation of modern aircraft engines it has been found desirable to enable the pilot to alter or adjust the fuel-air ratio for the purpose of obtaining lean mixtures under cerpurpose ofl conserving' fuel. The present invention also aims to make it possible for the pilot to change the setting of the automatic mixture control mechanism to cause this mechanism to maintain a leaner or a richer mixture pattern at the ilots l.lter the mixture by the same amount at all throttle settings, which would mean a different percentage change at every throttle setting and, consequently require frequent manipulation of the ratio adjusting lever by the pilot, but the obv:lect vofthe present invention is to provide that when the pilot changes the setting, this change shall be effected as a percentage change throughout a desired portion of the power range of the engine. In other words', the object is to enable fuel-air ratio mechanism by a selected or predetermined percentage'or proportion. 4

Should a combat aircraft be operating with the automatic mixture control manually set as `just described, to provide-aleen mixture, and, suddenly, under attack or otherwise, require full engine power, so that the pilot suddenly opens the throttle to full open position, or to any position corresponding to anengine power above the'cruising range, it is not only desirable but necessary for the'engine to return to operation on 'a full or maximum rich mixture pattern. Accordingly it is an object of the present invention to provide `for this contingency wlthout'attention from the discretion. Such'change in setting does not 1 pilot, other than the moving of the `throttle to full open position. That is to say, the present automatic mixture control aims to operate the engine on the full rich mixture characteristic pattern or curve of the engine whenever the engine throttle, momentarily to increase the fuel-airv ratio to cause the engine to accelerate quickly, the automatic fuel-air ratio control mechanism immediately, however, assuming control of the mixture. e] Y Another object of the invention is to provide for the adjusting of the fuel-air ratio at idling speed of the engine without affecting the mixture ratio at other speeds. Another object of'the invention is to provide for the adjusting of the fuel-air ratio at idling speed without interfering with the ability to cut oi! the fuel completely upon the stopping of the engine. i

In case of failure of the automatic mixture control mechanism properly to control the mixture, from any cause, it is desirable for the pilot to control the mixture manually. Accordingly another obiect of thepresent invention is to enable the pilot (preferablyby manipulation of the same lever which changes the setting of the automatic control mechanism to diiferent patterns) to adjust the fuel-air ratio by hand, should the automatic mixture control mechanism fail to operate.

A further object of the invention is to provide automatic fuel-air ratio control mechanism and, in addition, a manually operated fuel-air ratio control mechanism inter-related to one another in such a way that both mechanisms can be operated by a single lever at the pilots position.

A still further object of the present invention is to provide a fuel-air ratio controlling mechanism which will compensate for changes in temperature as nearly as possible in proportion to the extent of the temperature change.

The invention will be understood from a study of the accompanying drawings which show, by way of example, an embodiment of the invention as used in connection with an aircraft engine installation of the spark ignition type and in which the fuel is injected under suitable pressure into l the air induction conduit between the air throttle and the engine (non-timed injection). Alsothis engine is provided with a supercharging blower which raises the pressure of the fuel and air mixture above that of atmospheric pressure except when the engine is idling or developing very low power. It is to be understood, however, .that the improved mixture control apparatus may also be used with engines not provided with superchargers and where'the air is introduced into the cylinders entirely by suction. It will be understood also that the invention is capable of mechanical expression in other forms than the em- Referring now to the accompanying drawings;

Fig. 1 is a perspective view, partially diagrammatic, of a radial aircraft engine provided with the improved automatic mixture control apparatus of the invention;

Fig. 2 is a diagrammatic central vertical longitudinal section through the air intake conduit and supercharger;

Fig. 3 is a diagrammatic perspective View with certain parts in section showing the general arrangement and operation of the automatic mixture control mechanism.' the positions of certain parts not agreeing with the other figures;

Fig. 3a is a vertical section taken on the line Ict-3a of Fig. 3, the parts being set to provide automatic full rich operation;

Fig. 4 is an exploded" perspective view to be used in connection with Fig. 3 and showing certain of the parts of Fig. 3 separated from one another to facilitate a'n understanding of their arrangement and operation;

Fig. 5 is a vertical section taken on line 5 5 of Fig. 10 and shows a detail of a vane type servomotor forming a part of the control mechanism;

Figs. 6, 7 and 8 show other details and are diagrammatic vertical sections showing the connections for pressure liquid to the servomotor pilot valve; y

Fig. 9 is a vertical sectional view of the improved mixture control apparatus taken on the broken line 9-9 of Fig. 10 and illustrating the pressure responsive bellows diaphragm and parts actuated thereby;

Fig. 10-is a. horizontal section takenv on the plane indicated by lines I0-l0 of Figs. i3 and 15. passing through the hollow servomotor shaft and concentric pilot or control valve;

Fig. 11 is a horizontal section taken on broken lines ll--I I of Figs. 12 and 9 through the shaft for the hand setting lever; l

Fig. 12 is a vertical section taken on broken line I2-I2 of Fig. 10 showing the interior of the servomotor and part of the temperature compen- I sating mechanism; Y

Fig. 13 is a vertical section taken on broken line -Il of Fig. 12 through the setting lever shaft and the servomotor shaft and pilot valve;

Fia. 14 is a vertical section taken on broken line II-II of Fig. 10 showing the main operating spring h'ousing of the pressure responsive mechanism, and part of the temperature-compensating mechanism;

Fig. 15 is a vertical section taken on broken line' IS-IB of Fig. 11 looking in the direction of the arrows and showing the lever and ,linkage mechanism interconnecting the automatic mixture control mechanism, the air throttle and the h'and setting lever, the parts being shown in one position for starting the engine Fig. 15a is a diagrammatic view of the lever and linkage mechanism of Fig. 15 with the parts in a different position for starting the engine;

Figs. 15b, 15e and 15d are views similar to Fig. 15a with the Darts in positions' corresponding to three engine operating conditions under the control of the automatic fuel-air ratio mechanism:

bodiment illustrated and, consequently.zthat vthe invention is not limitedto'this embodiment but that its scope is indicated in the appended claims. u been stopped:

Figs. 15e, 15) and 15g are similar views sh'owing the parts in positions corresponding to the same thi-ee engine operating conditions but under manual (emergency) control of the fuel-air ratio:

' Fig. 16 is. a view ofthe lever end of the control mechanism casing to illustrate the manner of shutting of! the fuel supply after the engine has Fig. 17 is a vertical section similar to Fig. 3a but drawn to a larger scale and showing the parts set in the position -to provide automatic full lean operation: Y

Figs.`18, 18a, 18h, 18e, .18d and 18e show the automatic 'mixture leaning out mechanism in different positions corresponding to idling ad Y ratio characteristic shown in Fig. 19; and

Fig. 21 is a diagrammatic view of the temperature'compensating mechanism drawn to an enlarged scale to illustrate the manner of its operation. 1

Referring now to the accompanying drawings,

there is shown 'diagrammatically in Fig. 1 a

radial aircraft engine I having a shaft Z to receive vthe propeller and, at its rear end, a circular housing 3, the interior of whichA comprises a `manifold vfrom which radiate pipes t to the various cylinders of the engine. Within housing I there is also a rotary supercharger 5 having an impeller I driven from the engine and delivering 4the fuel and air mixture to the manifold. Within a casing 'I at the rear of manifold housing 3 there is a conduit 8 leading from the throttle -body 9 to convey the air and fuel mixture to the impelle'r E.. The induction pipe system is completed with an L-shaped air scoop or intake iii which has an opening facing toward the front of the engine and conveys th'e air to the throttle body-I within which is suitably pivoted an air throttlell..

Mounted at the rear of casing l, or in any other convenient position.. there is located afuel transfer pump I 2 which moves the fuel from the tanks tl'irough fuel line I3 to the engine. The fuel` from pump I2, through pipe Il, enters a variable capacity injection pump I5, driven by the engine, which is adapted to deliver the fuel under suitable pressure (usually several hundred pounds) through pipe I6 to the spray nozzle I'l by means of which the fuel is injected into conduit 8 between air throttle I l and the impeller B.. It will be understood that nozzle I'i may be arranged in any desired manner to obtain intimate mixture ofthe fuel vparticles and air, as, for

' example 'by directing the spray directly at the bellows diaphragm, corresponding to the fuel-air Injection pump ls is'provided with a capacity by means of link rods 26 and 27, lm kj connected to the lower end of actuating arm 28 which is nxed on one end of the pivot shaft of throttle valve member II.

The capacity control lever 22 of pump I5 is actuated to control the pump output, to produce the correct ratio of fuel and air,by means of the automatic mixture control apparatus contained in a housing indicated generally by numeral-28. This housing is provided with a suitable supporting flange 30 by means of which it may be bolted to a boss projecting from the front of throttle housing 9 or other suitable support.

Housing 29 contains mechanism which is responsive to variations in pressure and tempera- 'ture within the engine mammie t andv for this `reason the housing is sealed and its interior isl placed in communication with manifold 3 by means of a duct 3|. It will be understood that the connection of duct 3l with manifoldv sh'own in Figs. 1 and 2 is diagrammatic in character, as v this connection may be made atany point, or plurality of points, of the manifold to cause the pressure within housing 29 to vary as nearly as possible in accordance with the average pressure Within the manifold.

'remperatine variations within manifold a are registered by a temperature responsive element er 'elements (not shown) of the liquid expansion type suitably positioned with respect to the manifold to respond to changes in the temperature of the air or fuel-air mixture delivered to the engine by the supercharger. SuchV temperature responsive element, or elements, are vconnected with the interior of casing 28 by means of a capillary tube 32. The mechanism within casing 29 by means of which'such pressure and temperature variations are employed 4to eifect the shifting of the pump capacity lever 22 to control the fuel air ratio are to be described in detail below.-

'I'his mechanism has three external levers,

namely, pump control lever 33, pinned on shaft 36, throttle connection lever 35, pinned on shaft 3B, and a setting lever 31 for the mixture control :mechanism which is pinned 'on shaft Q38. Pump control lever 33 is connected to pump capacity lever '22 by means of a link rod 39. -Link rod 26 from throttle handle 2t and link 21 from throttle valve I I Vare both connected to throttle Acontrol lever 3d vso that this lever is actuated duit 8 on the intake side of the supercharger. 1

Nevertheless it will be understood that the pressure variations .on either side of the supercharger maybe used to operate the automatic mixture control mechanism. The mixture control mechanism within housing V29 is illustrated diagram-i maticaliy in the perspective views (Figs. 3 and 4) 'and comprises the following principal elements:

A. A duid pressure responsive mechanism indicated generally by numeral i3 (Fig.- 3) and comprlsing a bellows diaphragm Il (Figs. 3, 9 and 11), a main .actuating lever I5, the operating springs JQ and Il and the connected parts.

,.9 and 10).

nected to the bellows by a ball type universal B. A vane type servomotor indicated generally by numeral 45 having a hollow operating shaft 49 to which a driving member 59 having a driving lug 5I which engages a part secured to shaft 34 of pump control lever 33, to turn the same. Within hollow shaft 49 there is a rocking type pilot or control valve 52 for the servomotor.

provided with an operating crank 53 at its left hand end. y

C. A connecting and automatic leaning out mechanism indicated generally by numeral 54 through the instrumentality of which the uid pressure responsive mechanism 43 actuates the pilot valve 52 of servomotor 49.

D. Fuel-air ratio control for quick acceleration, and for starting the engine which comprises ,p

the floating fulcrum lever and linkage mechanism shown at the right hand portion of Fig. 3 and -in Fig. 15. p

E. A manual emergency mixture control mechanism comprising the floating fulcrum lever and linkage mechanism just referred to and certain additional parts cooperating therewith.

F. A temperature compensating mechanism indicated generally by reference numeral 55 which cooperates with the pressure responsive mechanism 43 in actuating the connecting and leaning out mechanism 54 and, through this. the servomotor pilot valve 52.

The fluid pressure responsive mechanism Actuating lever 45 is the main operating lever of this mechanism and is fulcrumed in an interior part of housing 29 for rocking movement l about a center 55. Lever 45 is actuated by bellows diaphragm 44 through a connecting rod 51 hinged at 55 to the short arm of lever 45 extending from the right or fulcrum 55 (Figs. 3,

The upper end of rod 51 is con- Joint, of which the lower socket member 'is held in engagement with the ball, by means of a heavy spring 51.

0n the longer left hand portion of lever 45 there is pivoted at 59 a triangular lever 55, and hinged to this lever at 5I is the main actuating link 52 for the control mechanism, which is hinged at its upper end at El to operating lever 54 of the connecting and leaning out mechanism .A

54. This mechanism, which will be described in detail later, has a pilot valve-actuating lever 55 actuating lever 4-5 thereby making the motion of lever 52 the same as though it were hingedl directly tolever 45.

fIn the engine under consideration the manifold pressure varies from a minimum of about 15" Hgabsolute to a maximum of about '10" Hg, it being understood that this range of pressure may vary in accordance with the particular engine on which the mixture control apparatus is to be installed. Bellows 44 is arranged to operate under compression only and consequently is sealed at a pressure of about 12" Hg, that is,

from 2" to 3" Hg below that corresponding to the lower end of the manifold pressure range. In Figs. 3 and 9 of the drawingsbellows 44 is shown inlits fully extended condition, that is, corresponding to a pressure of 15" Hg. Hence as the manifold pressure increases the bellows 44 is compressed to a greater and greater extent thereby raising the right hand end of lever 45 and lowering its left hand end.

The fluid pressure acting on bellows 44 is balanced by means of a main operating spring 46 and is accessible from the exterior of housing y of casing 55 is limited by an adjustable stop screw 14, also accessible from 'the exterior of casing v 29, which constitutes a means for adjusting the mixture ratio at the idling speed of the engine, as will appear later on.

Referring now to Fig. 19, curve A shows the characteristic fuel-air ratio pattern for maximum or full rich mixture operation of the particular engine upon which the control shown in the drawings is to be used. That is to say, curve A shows the variation in the full rich fuel-air ratio of the engine throughout its power and .an extent. To control or regulate the capacity control lever 22 of fuel injection pump I5 in such a way as to bring about such a variation in the fuel-air ratio `throughout the range of manifold pressure corresponding to the range of speed and power of the engine presents a considerable problem. v

The output of pump i5 increases or decreases proportionally with changes in engine speed, so that, for any given, or constant, setting of the engine throttle, the fuel-air ratio isautomatically controlled merely bythe change in speed of the pump, but the problem is to regulate this ratio so as to make it follow closely the engine characteristic as the throttle is opened or closed to a great er or less extent. l h

To accomplish this, the force employed to balance the fluid pressure on bellows diaphragm 44 is made to vary with change in manifold pressure in a predetermined manner from the minimum pressure (corresponding to idling speed) to the maximum pressure (corresponding to full throttle opening or full engine power and speed), and in such a way as to cause the proper actuation of operating lever 54 and pilot valve 52 (and aasaeer consequently pump capacity 4lever 22) to bring about the change in fuel-air ratio according to the characteristic pattern of the engine, such, for example, as shown in curve A of Fig. 19, it being understood that equal displacements of pilot valve 52 (and lever 22) cause substantially equal changes in the output of'fuel pump i5.

In Fig. 20 there is shown at curve C the variation justdescribed in the force required to balance bellows 44 from its -Iully extended condi-v tion corresponding to the minimunrmaniiold pressure to its fully compressed condition corresponding to the' maximum manifold pressure. 'Ihat `is to say, the torce-displacement curve C corresponds to the engine characteristic curve A, Fig. 19. The shape of curve C therefore depends upon the construction of the particular engine, or type ofengine. with which the mixture control is to be used. l

The proper variation in balancing force according to curve C of Fig. 20 ior balancing the fluid pressure on bellows '44 is obtained by the coaction 'of springs 4t and 41. Iii/Fig. 20 the balancing force suppliedv by spring` t6 is indi-- cated by curve D. 'This curve, however. coincides withcurve C only at two points, namely, its opposite ends. `In other words, the force supplied 'by spring it is correct onlyat idling speed and at full throttle opening; in between these points a greater and a varying force is required.`

'.lhis additional force is provided by means of auxiliary spring lll operating through the mechanism shown particularly in Figs. 3, 9, 12 and 14. Spring lll is mounted within a. casing 'it over the outside of which a lower sleeve 'It is telescoped. .The lower end of spring tl rests on the bottom of sleeve i6 and the position of this `sleeve is adjustable vertically by means of an adjusting screw 'll accessible from the ex-v terior of casing 29 and locked by means of a nut lll. Spring tl tends to urge casing lli upwardly transmitting itsiorce to an arm 'lt secured to a member lit which hase. second arm 8i projecting vertically at substantially right angles to armr lt. Arm di at its upper end has a laterally projecting pin t2 carrying a grooved roller tl which coacts with a cam tt secured to tubular casing tt oi main spring tt. Vlilleinber tu is mounted for rocking movement on a xed shaft @t segured in one of the outside walls of housing By virtue-of the mechanism just described inacteristic pattern required by the engine.

From this descriptionit will be understood l that the shape oi' the fuel-air ratio curve can be cludingcam lift and roller dit a varying force is g transmitted to actuating lever dit of the pressure-responsive mecm and the shape of earn itt is so arranged as to cause this force, when added to the force ci spring et, to produce a total' force which variesaccording to curve C oi Fig. 2li. '.l one point Z on curve C. for example, this corresponds to a force of approximately 60 pounds required to balance the duid pressure operating on the bellows when compressed by an amount indicated by the length of the line 0X;v This force is made up' of a force oi approximately li5 pounds, produced by main springtt, to which is added a` force of approximately 15 pounds which is provided by auxiliary spring tl'y acting through roller at and cam tt.

Stating it in another way, the resultant force provided lby the two springs Wand 4l opposing the action oi the manifold pressure onbellows i4 is modified by the action of cam 84 and roller Min 4such a way as to bring about 4the control or `regulation of-pilot valve 52 to produce variaadjusted within certain limits by changing the compression of springs 46 and 4l by means of adjusting screws I0 and 11; also that if the desired result cannot be obtained in this way, then cam 84 can be replaced with another cam having a diierent proiile. By such adjustments the mechanism can be adapted for operation with any particular engine or type of engine.

`The seroomotm` servomotor 40 has vane 86 projecting from one side of a circular hub 8l (Fig. 4) which is keyed or otherwise securely fixed to the hollow operating shaft 49 of the servomotor so that movement of the vane causes movement of driving member 50 and driving lug 5i. Vane t6 divides the servomotorfchamber into two 'compartments 88 and- 89 which are separated from one another on the rear side of hub tl by means of a land 90 coactingwlth the hub.

At the right of the servomotor, as viewed in Figs. '3 andv 4, the motor shaft t9 is arranged to turn in a bore through the end wall- 9| of the servomotor chamber. Ihe wall 92 atthe left of the chamber has a projecting portion 93 considerably larger than shaft 49 through which extends a cylindrical bore ,also much larger than shaft t9. Fixed in this bore is a bushing et and arranged for turning movement within bushing Vt4 (for apurpose to be described) there is a sleeve member 95 having a flange t .at its inner end bearing against the servomotor hub nl. Within sleeve tu is the operating shaft i9 and withinthis shaft is the pilot valve 52, as previously explained.

The servomotor is operated by liquid under suitable pressure supplied through a duct tl and, after passing through, the motor, is returned to the liquid supply through a second duct tt. These ducts are shown extending up wardly and to the left of the vane motor in Figs. 3 and t but in the actual construction are at the bottom of the servomotor as shown Fig. 13.

AThe operating liquid, such as oil, from the engine lubricating system, passes from inlet duct tl through a' hole 99 in bushing @t (Figs. d and (i), thence through an elongated aperture or part ttt, the purpose of which will appear later, in sleeve td and into a circular groove lul in motor shaft de. The oil then passes through a series of four holes m2 spaced around shaft t9 in thebottom of groove iti and communicating with a. second circular groove itt in pilot valve di. v Y

Opening out of this second circular groove itl? are` two diametrically opposite channels tot (Figs. d, l2 and 13) extending longitudinally of pilotvalve (i2. These channels extend a. limited distance along the surface of the pilot valve to passes through channels |01 to the spacing its 

